One of the more serious problems faced by child welfare services involves the management of children with serious behavioral and mental health problems. Aggressive and defiant foster children are more likely to have multiple foster care placements, require extraordinary social services resources, and have poor short- and long-term mental health outcomes. Interventions that work with challenging foster children and enhance foster parents' skills in managing problem behaviors are necessary. This article presents the successful results of a single case study examining the application of Parent-Child Interaction Therapy (PCIT) with an aggressive young boy and his foster-adoptive parent. PCIT is a dyadic intervention that has been identified as an empirically supported treatment for abused children and for children with different types of behavioral disruption. The application of PCIT to assist foster parents is a promising direction for child welfare services. (Contains 1 table and 2 figures.)